FOSSIL ANGIOSPERMS 277 



definiteness to modern groups are fairly submerged by the ex- 

 tinct and vague types. Such a plexus is consistent with any 

 evolutionary theory of the origin of Dicotyledons, and that it 

 has been definitely discovered in the Lower Cretaceous is of 

 great importance. 



Proangiosperms. — These are the vague forms referred to 

 above as being not definitely Dicotyledons but suggestive of 

 them. They are recognized by stem-structure and leaf-vena- 

 tion, and seem to be related to numerous modern families, 

 being good illustrations of so-called " comprehensive types." 

 It is hardly to be doubted that many of them represent primi- 

 tive Dicotyledons. If the Lower Cretaceous be divided into 

 five periods, the Proangiosperms not suggestive of modern 

 groups are the only dicotyledonous forms in the first. In 

 the other periods they also occur, but in diminishing impor- 

 tance as compared with the increasing number of recognizable 

 forms. These clearly antecedent and for a time associated 

 forms are very suggestive of their significant relation to modern 

 Dicotyledons. 



Forms suggestive of Modern Groups. — After the first period 

 of the Lower Cretaceous, forms suggestive of modern groups 

 appear. They are so clearly Dicotyledons as not to be included 

 among the Proangiosperms, but they are just as distinctly not 

 modern types. Their generic names suggest the modern resem- 

 blances, but these must not be taken to indicate relationships. 

 For example, such names as Leguininosites, Menispermites, 

 Myrsitwpihyllum, Proteophyllum, Peucedanites, etc., tell of cer- 

 tain superficial resemblances, but may be very far from indi- 

 cating real relationships. 



Modem Genera. — As already stated, no modern genera were 

 associated with the Proangiosperms during the first period of 

 the Lower Cretaceous. In the second period, however, an ex- 

 tinct species of Populus has been recognized, the most ancient 

 living genus of Dicotyledons known. In the third period Mag- 

 nolia and Liriodendron are recorded; in the fourth Salix, Aris- 

 tolochia, Sassafras, Adoxa, and Aralia appeared ; and in the 

 fifth Myrica, Laurus, Eucalyptus, and Viburnum arc recorded. 



In considering this record of the Lower Cretaceous the fol- 

 lowing thing- become evident: 



1. The genera, so far as they are identical with living gen- 



